Stents are used for a variety of medical purposes in the body including in the coronary arteries, the peripheral arteries, arteries of the neck, cerebral arteries, veins, biliary ducts, urethras, ureters, fallopian tubes, bronchial tubes, the trachea, the esophagus and the prostate. Stents are typically placed or implanted within a bodily vessel, for example, for treating stenoses, strictures or aneurisms therein. They are implanted to reinforce collapsing, partially occluded, weakened, or dilated sections of a blood vessel.
Stents are typically available in self-expanding configuration and mechanically expandable configuration. Hybrid stents which are self-expanding in part and mechanically expandable in part are also available.
Many stents are manufactured with struts having a zig-zag or serpentine configuration which resembles that of a sine wave. An example of a serpentine portion of a stent is shown at 104 in FIG. 4a. Serpentine portion 104 extends about the circumference of the stent and includes a plurality of turns 105 which extend between adjacent struts. The individual struts are oriented at an angle Θ1 relative to longitudinal axis 101 of the stent. When a stent comprising one or more of serpentine portions 104 is radially expanded from an unexpanded state to an expanded state, as shown in FIG. 4b, the angle Θ2 of the struts increases relative to the longitudinal axis and the effective strut length decreases from L to L-ΔL resulting in foreshortening of the stent.
Foreshortening of stents during deployment, however, is undesirable, as it reduces the placement accuracy of the stent. There remains a need for innovative stents which do not foreshorten upon expansion.
Further, it is often desirable to deliver drugs into a patient's body to treat medical conditions. In particular, a variety of drug therapies are available for treating the coronary system, either alone or in combination with more invasive procedures. Such therapies may include delivering substances, such as nitroglycerin, epinephrin, or lidocaine, endocardially or into the pericardial space to treat the coronary system. In addition, heparin, hirudin, ReoPro® or other anti-thrombotic compounds may be infused into blood vessels associated with the coronary system, such as occluded coronary arteries, or elsewhere in the cardiovascular system. More recently, gene therapy, e.g. introducing genetic material, and growth factor therapy, e.g. introducing proteins, cells or vectors including angiogenic growth factors, have been demonstrated to provide potential benefits in treating ischemic heart tissue and other regions of the coronary system, for example, by stimulating growth of neovascular conduits, which may evolve into new blood vessels.
Various methods have been used to introduce drugs into the vasculature including, for instance, infusion catheters which may be optionally equipped with either a porous perfusion balloon, and/or with an electrode and/or heating element to improve localized delivery for continuous or intermittent delivery, ionophoresis in which a first electrode may be provided within a perfusion balloon, and a second electrode provided on an external region of the patient's body near the artery, embedding or depositing a drug on a catheter wall, a non-porous balloon wall on the catheter and/or a coating on the catheter, and so forth.
Another method of drug delivery has been to employ a stent. U.S. Pat. No. 6,258,121 describes, for example, a stent having a polymeric coating for controllably releasing an included active agent.
Without limiting the scope of the invention, a brief summary of the invention is set forth below. Additional details of the summarized embodiments of the invention and/or additional embodiments of the invention may be found in the Detailed Description of the Invention below.